Franklin County, WA Accessory Structures: ADU Owner Occupancy (2026)

050 of the Franklin County zoning code authorizes one accessory apartment per single-family dwelling in single-family zoning districts, subject to a list of conditions. Subsection G states plainly that one dwelling must be owner-occupied for eight months of the year. Because the accessory apartment must share the same roof as the principal dwelling under Subsection B, the owner-occupancy condition effectively requires the property owner to live in either the main house or the attached apartment for at least eight of the twelve months in a year, closing off the option of renting both units to non-owner tenants simultaneously.

The requirement sits alongside other conditions in the same section: the apartment must have its own exterior entrance separate from the main entrance, its own kitchen and bathroom with no more than two bedrooms, and cannot exceed 40 percent of the principal dwelling's floor area or 800 square feet. An accessory dwelling permit, required under Subsection L before any building permit issues, is the mechanism the Planning and Building Department uses to confirm compliance with the owner-occupancy condition at the time of approval. Accessory dwelling units that lawfully existed before the ordinance codified in Title 17 took effect are treated as legal nonconforming uses under Subsection M, but those units are still required to obtain an accessory dwelling permit, which brings the owner-occupancy condition forward even for older, previously unpermitted apartments.